During the past decade developing alternative sources of fuel has become an increasing concern for both environmental and economical reasons. Fossil fuels are the traditional source for fueling gas turbine power generating systems. Sources for fossil fuels are becoming scarce and expensive, and concern has arisen about the environmental impact the byproducts of processing these fuels have.
In general, an electric power producing turbine system includes an air compressor, a combustion chamber for burning fuel in the presence of the compressed air, a turbine into which the high pressure combustion gases are flowed to expand and produce power, and an electric generator which is powered by the turbine.
In an effort to solve the problems of fossil fueled power plants, research has been conducted in using biomass to fuel a turbine system. Wood, in the form of saw dust, and sugar cane bagasse have proven to be viable options for fueling turbine systems. Wood and sugar cane are renewable fuels and the burning of these fuels does not have the negative environmental impact which the traditional fossil fuels have.
In developing a system for burning biomass several problems must be overcome. Biomass of the types mentioned above have a much higher combustion temperature than traditional fuels. The combustion chamber must be constructed to withstand such high heats associated with burning these fuels. Controls and sensors must be located throughout the system to avoid serious damage to the entire system from overheating. Because the combustion chamber is both pressurized and maintained at a high temperature, special attention must be paid to how the biomass is fed into the combustion chamber. The feeder system must be able to transport the wood particles from a zone of low pressure to a zone of high pressure while supplying means to protect the feeder system from the high temperature of the combustion chamber.
Another problem associated with utilizing biomass as a fuel is that one of the byproducts of burning biomass is ash. If the ash is not removed before the combustion gases enter the turbine, the ash will adhere to the turbine blades and clog the system, seriously degrading the performance of the system and damaging the turbine. Removal of all of the ash is extremely difficult, therefore, other actions must be taken to prevent the remaining ash from adhering to the turbine blades.
An additional concern is the life of the turbine blades. To extend the life of the turbine, the temperature of the combustion gases entering the turbine must be controlled. Because the turbine inlet temperature must be controlled or limited a flow enhancer must be utilized to attain the power output needed.
A final concern is the sudden loss of load which occurs when there is a disconnection of the electrical generator from a power distribution grid. A load replacement device must be incorporated into the system to avoid the overspinning of the turbine.
U.S. Pat. No. 4,409,786 discloses a wood burning system and method. The system and method discussed in this patent does not approach the problems that occur with a system to be used commercially. In the wood burning system discussed there are no means to control the pressure in the combustion chamber to avoid overheating of the system. The temperature of the gases exiting the combustion chamber is not cooled to a point that the remainder of the system can tolerate. The patent does approach the problem of the removal of ash but assumes that all ash will be extracted from the combustion gases, which is not the case. No supplemental methods are provided for dealing with the ash remaining in the combustion gases. The life of the turbine is a major concern for a system to be used for an extended amount of time. To extend the turbine life the temperature of the gases entering the turbine must be controlled which means power output is sacrificed. No solutions are provided for retaining a certain amount of power output when the inlet turbine temperatures are limited. Another concern is the loss of load due to a disconnect from the outside facility. The system discussed in the patent does not approach the problem of preventing the turbine from overspeeding due to loss of load. Finally, a central control system is necessary to monitor and control critical aspects of the system while operating. A central control system is not discussed or presented in the '796 patent.
Therefore, it is an object of this invention to provide a system for burning biomass to fuel a gas turbine which provides a means to control the pressure in the pressurized combustion chamber.
It is a further object of this invention to provide such a system which provides a means to cool the temperature of the combustion gases exiting the combustion chamber.
It is yet a further object of this invention to provide such a system in which the ash of the combustion gases does not adhere to the turbine blades.
It is still a further object of this invention to provide such a system where a flow enhancer is utilized to increase the energy required to power the system.
A further object of this invention is to provide such a system where a load replacement device is incorporated to absorb the load of the system when the outside load is suddenly disconnected.
It is yet a further object of this invention to provide such a system that incorporates a central control system to monitor and control the system.